The present invention is directed towards a leader used to pull a seamable papermaker""s fabric onto a paper machine particularly one that is durable and allows its reuse.
Fabrics in modern papermaking machines may have a width of from 5 to over 33 feet, a length of from 40 to over 400 feet and weigh from approximately 100 to over 3,000 pounds. These fabrics wear out and require replacement. Replacement of fabrics often involves taking the machine out of service, removing the worn fabric, setting up to install a fabric and installing the new fabric. While many fabrics are endless, about half of those used in press sections of the paper machines today are on machine seamable. All dryer fabrics used all have a seam of some type. Some Paper Industry Process Belts (PIPBs) are contemplated to have an on machine seam capability, such as some transfer belts, known as Transbelt(copyright). Installation of the fabric includes pulling the fabric body onto a machine and joining the fabric ends to form an endless belt.
An important aspect of loading a fabric body onto a paper machine is that there be uniform tension across the fabric. If uniform tension is not achieved and one section of the fabric pulls more than another, then the fabric can bubble or ridge across the fabric width.
Another aspect of loading a fabric body is preventing damage to the fabric body seam. In order to avoid or minimize the chance of damage to the seam during installation, tension, weight and pressure must be avoided on the seam itself.
A further aspect of loading a fabric, especially very long ones is properly aligning the fabric body in the machine so the fabric guides true in the machine direction (MD) and does not oscillate or track to one side of the machine. If the fabric guides or tracks poorly it can make contact with the paper machine support frame and cause fabric damage.
For fabrics and belts with seams that can be joined together on the paper machine, various types of leaders have been tried to assist installation. In order to avoid or minimize the potential for damaging the fabric body and the machine during installation and operation, the leader should be designed so there is uniform tension across the fabric body. There have been several attempts to design such leaders.
U.S. Pat. Nos. 5,306,393 and 5,429,719 both to Rhyne describe a device and method for installing a fabric body onto a paper machine. The method includes providing a self-aligning fabric loading harness having a leading edge and a plurality of spaced empty grommets disposed adjacent to the leading edge, to which multiple ropes are attached, securing a pull rope through loading harness and a line receiving device, pulling the pull rope, and automatically readjusting the pull rope through the loading harness to attempt to achieve uniform tension across the fabric.
Some leaders are square or rectangular, with the long dimension to either the MD or CD. Multiple ropes or straps are attached to the leader at evenly spaced apart locations across the width of the leader, and the leader with the attached papermaker""s fabric or belt is pulled through the fabric run, and the ends of the papermaker""s fabric or belt are brought together and joined by a seam to make the fabric endless. The leader is removed and the fabric is ready for use. However, the multiple ropes or straps can get hung up on the stationary equipment in the fabric run, causing difficult and time consuming installation, if not tearing and damage of the fabric.
There are also leaders currently used in the industry which are shaped like an isosceles triangle, having the apex removed to form a trapezoid. The leaders are fabricated from a woven material. The material can also be a nonwoven from which the leader is fabricated. The base of a leader has a zipper, which is used to attach the leader to an end of the fabric being installed on the paper machine. Such a design is preferred because only one rope is attached near the apex to pull the fabric onto the machine. When the triangle is cut from woven material, one of the yarn systems in the weave goes straight from the base to the apex and the other is at a 90xc2x0 angle thereto.
FIG. 1 shows a top view of a prior art leader 10. Leader 10 is shaped like an isosceles triangle and is fabricated from a woven material. The base 12 of leader 10 has a one half a zipper edge 12, which is used to attach leader 10 to an end of the fabric being installed on the paper machine to which the other half of the zipper edge is attached to the fabric or belt. Papermill personnel can attach a rope near the apex which is provided with a hole 14 and pull the fabric onto the machine. When the triangle is cut from woven material, one of the yarn systems in the weave goes straight from the base to the apex and the other is at a 90xc2x0 angle thereto. When the rope is pulled as shown in FIG. 1a, the force is unevenly distributed across the leader as well as the attached fabric body which causes fabric body to bunch up on the sides.
Full width steel bars may be inserted at the base of the leader for better weight/tension distribution. However, the bars are heavy, thick and sometimes difficult to pass through the nip formed by two press rolls, or a shoe and opposing roll.
With a leader of this type, even with a 4 foot wide (in the cross machine direction or CD) steel reinforcing bar at the apex of the triangle/trapezoid, when the rope is pulled the force is unevenly distributed about the leader and across the attached fabric body. When the apex above is pulled, most of the force is distributed over four feet in the CD at the center of the leader. This causes the center of the fabric to bunch up, making it more difficult to seam, and often causes the edges of the fabric or belt 16 and leader 10 to droop 18 and 20 while it is being pulled onto the paper machine.
The drawback of this type of leader is that the load is always concentrated down its center. This causes both the center of the leader and the fabric attached to it, to lead the edges and form waves in the center while pulling through the machine, making it more difficult to seam as well as guide the fabric through the run during installation. This often causes the edges of the fabric to droop while it is being pulled through the fabric run. Any fabric edge droop or bunching/waviness (any departure from a relatively flat fabric profile) can cause the fabric to become hung up on stationary equipment, or to not easily pass through the gap formed between two press rolls. Attempts to correct both the fabric and leader edges from drooping by inserting ropes down the edges, usually results in the edges curling up and folding over, which is also not desirable.
While the types of methods and devices for installing an on machine seamable fabric or belt aforementioned have particular advantages, they also have attendant disadvantages discussed above.
It is therefore a principal object of the invention to overcome the shortcomings of the devices heretofore mentioned.
It is a further object of the invention to provide a device and method for installing a fabric in a paper machine which evenly distributes the load on the fabric making for easier installation and seaming.
It is a further object of the invention to provide a device for installing a fabric in a paper machine which is durable and allows for repeated use.
To solve this problem, a leader has been fashioned from at least one section of a polymeric material to form a triangle with a tapered apex. The triangle is preferably isosceles with the total leader length equivalent to the base of the leader width divided by 1.5. In preferred embodiments the leader comprises polymeric PVC (poly-vinyl-chloride) coated woven coarse fabrics woven of polyamide or polyester yarns, usually monofilaments, which are assembled together by a high frequency (H.F.) welding system. In a more preferred embodiment, additional melted strips of PVC are placed at regular intervals to reinforce the leader structure. There is a loop formed of folded over material provided at the tapered apex so that a metal bar may be placed therein with an access hold cut around a portion of the bar in the center to allow a rope or other means to be affixed to pull the leader. Depending on the fabric weight, load distribution achieved, and strength of the leader material itself, more than one rope might be attached at the apex.
The leader is attached to the fabric by an attachment means at its base. In a preferred embodiment, the leader is attached to the fabric by a zipper, one half of which zipper edge is attached to the base of the leader. Another half of the zipper is attached to the fabric. Other means suitable for this purpose might be used to attach the leader to the fabric.